Constellations of satellites having inclined, elliptical orbits are useful for providing communication coverage to Earth. One approach to providing continuous coverage uses two or more satellites having the same ground track. To ensure that the satellites have the same ground track, a fixed angular separation is maintained between the ascending node of each orbit (the intersection of the orbit with the equatorial plane of Earth where the satellite crosses from the southern hemisphere into the northern hemisphere). The ascending nodes of the orbits may be equally or unequally spaced, depending upon the mission requirements. Because each satellite orbit therefore has a different position with respect to the Earth, the sun and the moon, gravitational effects of these bodies perturb the orbit of each satellite to a differing degree, causing each orbit to tend to precess around the Earth at a different rate. This precession is measured as a drift rate in the right ascension of the ascending node (“RAAN”) of each orbit. These perturbations also affect the other orbital elements, such as the argument of perigee, the semi-major axis, the eccentricity, the argument of perigee and the inclination.
Because the RAAN drift rate for each orbit in a constellation is prone to varying at a different rate, the orbits, if left uncorrected, would tend to lose their fixed angular separation. Accordingly, stationkeeping fuel stored onboard each satellite must be expended in controlled engine burns to maintain a single RAAN drift rate for all of the orbits, as well as to maintain the other orbital elements of the satellite orbits. If the effects of these orbital perturbations could be minimized for the constellation, the satellites would require less stationkeeping fuel onboard, permitting a greater payload mass for a given launch vehicle.
Accordingly, there is a need to optimize inclined, elliptical satellite constellations with a shared ground track to experience less orbital perturbations and to require less stationkeeping fuel. The present invention satisfies these needs and provides other advantages as well.